Move MLX tests from math to elemwise

[Mr-Imperium]

Description

Moved 9 elementwise test functions from test_math.py to test_elemwise.py
Added necessary imports (erfc, erfcx, isnan, softplus) to test_elemwise.py
Kept 3 non-elementwise tests in test_math.py (dot, int_div_specific, max_and_argmax)
Both files compile successfully without syntax errors

Related Issue

• Closes MLX tests: Elemwise tests in test_math.py #1730
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

[ricardoV94]

Thanks @Mr-Imperium

I left some comments above

[Mr-Imperium]

@ricardoV94 I've worked on them. Thankyou for the review!